Bypass block for unregulated gearboxes

ABSTRACT

A bypass apparatus for lubricant in an unregulated pressurized gearbox including: a block including a lubricant inlet in fluid communication with a pressure relief valve, wherein the pressure relief valve diverts lubricant into the gearbox or into an oil filter, wherein lubricant is returned to the gearbox when the lubricant is cold and/or pressure at the pressure relief valve is high to reduce damage to the gearbox caused by high pressure during a cold start, and when the lubricant temperature increases and the pressure is reduced the pressure relief valve closes and lubricant enters the oil filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a divisional patentapplication of U.S. patent application Ser. No. 15/967,884 filed on May1, 2018, which is hereby incorporated by reference in its entirety.

This patent application is related to U.S. provisional patentapplication Ser. No. 62/399,067 filed on Sep. 23, 2016 entitled“Improved Helicopter Transmission System” and U.S. provisional patentapplication Ser. No. 62/423,371 filed on Nov. 17, 2016 entitled“Improved Helicopter Transmission System,” all of which is herebyincorporated by reference in its entirety.

STATEMENT OF FEDERALLY FUNDED RESEARCH

None.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of gearboxes, andmore particularly, to a method of installing a pressure relief or bypassvalve in a previously unregulated pressurized gearbox or a newlydesigned pressurized gearbox.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is describedin connection with gearboxes.

Since their inception, rotorcraft and rotorcraft drive systems have beenimproved to reduce the possibility of failure during flight. Toward thatend, a number of modifications have been made to drive systems toimprove reliability. However, despite advances in materials and design,a number of failures continue to occur that affect rotorcraftperformance. One example of a problem with current rotorcraft drivesystems is that, in some instances, the failure of single drive systemcomponent leads to failure of the entire drive system. Another exampleis a loss of lubrication event that causes the loss of torquetransmission by drive system subcomponents such as gearboxes oraccessories connected to the main rotor gearbox.

More particularly, the failure of a single gearbox or shaft connected tothe main rotor gearbox can significantly impact operations. For example,if there is a loss of lubrication to a gearbox, the gearbox loses torquetransmission, causing damage to upstream or downstream components. Thesame can occur when a shaft becomes unbalanced (or breaks), which candamage couplings, gearboxes and even the main rotor gearbox.Unfortunately, when a portion of a drive system experiences a failure orreduction in performance, the concomitant reduction in power leads tochallenges with flight performance.

One such system is taught in U.S. Pat. No. 8,752,673, issued toThivierge, et al., and entitled “Lubrication system with porouselement.” These inventors are said to teach a lubrication system for agas turbine engine that includes at least one porous element located ina cavity containing at least one rotating component receiving a flow ofthe lubricant, the porous element being located across a path taken by aportion of the lubricant expelled from the at least one respectiverotating component such that the portion of the lubricant circulatestherethrough, the at least one porous element being made of a materialresistant to a temperature of the lubricant, and the at least one porouselement reducing a velocity of the portion of the lubricant circulatingtherethrough.

Another such system is taught in U.S. Pat. No. 6,058,694, issued toAckerman, et al., and entitled “Gas turbine engine commanded oil flowvalve with failsafe.” These inventors are said to teach an improved oilflow reduction valve regulates the flow of lubricant to a fan reductiongearbox of a turbine engine, or other accessories requiring lubricationas a function of engine load. The invention is said to take advantage ofthe strong correlation between the gear torque output of the engine andthe engine compressor discharge pressure by metering oil flow as afunction of compressor discharge pressure. In one embodiment a meteringvalve employs a sense piston that receives a pressure signal from thecompressor section of the engine. In response to the pressure signal,the sense piston moves a slide valve, which blocks or uncovers one ormore output orifices to regulate the flow of oil through the meteringvalve. The valve is preferably configured to allow maximum oil flow inthe event the valve should fail or in the event the compressor dischargepressure signal is lost, to ensure safe operation of the lubricatedcomponents.

The drawbacks of prior art gear lubrication systems, make systems andmethods of improving the reliability of pressurized gearboxes desirable.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a bypass apparatus forlubricant in an unregulated pressurized gearbox including: a blockincluding a lubricant inlet in fluid communication with a relief valve,wherein the relief valve diverts lubricant at high pressure into thegearbox or at low pressure into an oil filter, wherein lubricant isreturned to the gearbox when the lubricant is cold and pressure at therelief valve is high to reduce damage to the gearbox or the oil filtercaused by high pressure during a cold start, and when the lubricanttemperature increases and the pressure is reduced the relief valvecloses and lubricant enters the oil filter. In one aspect, the bypassblock is upstream from an oil filter. In another aspect, the reliefvalve is a pressure relief valve and relieves pressure down to 250 psior any preset value. In another aspect, the gearbox is an intermediategearbox, a tail rotor gearbox, or a reduction gearbox. In anotheraspect, the relief valve is at least one of: mechanical, electronic,magnetic, or spring-loaded. In another aspect, the relief valve is apressure or temperature activated valve. In another aspect, the reliefvalve is a pressure relief valve. In another aspect, the relief valve isboth activated by pressure and temperature. In another aspect, therelief valve is a pressure relief valve, a pressure release valve, apressure safety valve, a safety relief valve, a pilot-operated reliefvalve, a snap acting release valve, a pop-it valve, or a modulatingrelease valve.

In another embodiment, the present invention includes a method forreducing lubricant damage to an unregulated gearbox including: providinga block including a lubricant inlet in fluid communication with a reliefvalve, wherein the relief valve diverts lubricant into the gearbox orinto an oil filter; diverting the lubricant into the gearbox when thelubricant is cold and pressure at the relief valve is high to reducedamage to the gearbox or the oil filter caused by high pressure during acold start, and closing the relief valve when the lubricant temperatureincreases and the pressure is reduced the relief valve closes andlubricant enters the oil filter. In one aspect, the bypass block isupstream from an oil filter. In another aspect, the relief valve is apressure relief valve and relieves pressure down to 250 psi or anypreset value. In another aspect, the gearbox is an intermediate gearbox,a tail rotor gearbox, or a reduction gearbox. In another aspect, therelief valve is at least one of: mechanical, electronic, magnetic, orspring-loaded. In another aspect, the relief valve is a pressure ortemperature activated valve. In another aspect, the relief valve is apressure relief valve. In another aspect, the relief valve is bothactivated by pressure and temperature. In another aspect, the reliefvalve is a pressure relief valve, a pressure release valve, a pressuresafety valve, a safety relief valve, a pilot-operated relief valve, asnap acting release valve, a pop-it valve, or a modulating releasevalve.

In another embodiment, the present invention includes a bypass apparatusfor lubricant in an unregulated gearbox including: a block including alubricant inlet in fluid communication with a pressure relief valve,wherein the pressure relief valve diverts lubricant into the gearbox orinto an oil filter, wherein lubricant is returned to the gearbox whenthe lubricant is cold and pressure at the pressure relief valve is highto reduce damage to the gearbox caused by high pressure during a coldstart, and when the lubricant temperature increases and the pressure isreduced the pressure relief valve closes and lubricant enters the oilfilter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures and in which:

FIG. 1 shows a side view of a helicopter according to a preferredembodiment of the present application;

FIG. 2 shows a partial cross-section, perspective view of helicopteraircraft according to an alternative embodiment of the presentapplication;

FIG. 3 shows an isometric view of a gearbox lubrication system thatshows the position of the bypass block of the present invention;

FIG. 4 shows a contralateral isometric view of the gearbox lubricationsystem that shows the position of the bypass block of the presentinvention;

FIG. 5 shows a cross-section view of the bypass block of the presentinvention;

FIG. 6A is a close-up, cross-sectional view of a pressurized filter thatis lacking the bypass of the present invention and is connected togearbox; and

FIG. 6B shows a close-up, cross-sectional view of a pressurized filterthat includes a bypass block.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the system of the present application aredescribed below. In the interest of clarity, not all features of anactual implementation are described in this specification. It will ofcourse be appreciated that in the development of any such actualembodiment, numerous implementation-specific decisions must be made toachieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

The present invention relates to a lubrication fluid bypass forpressurized but unregulated gearboxes. More specifically, the presentinvention addresses the need for optimizing lubrication fluid flowduring various stages of operation of a gearbox. One such example of agearbox is an intermediate gearbox of a rotorcraft. Generally, gearboxesare separated into those that are splash lubricated gearboxes, where nooil pressure is present, and those that are pressurized and in which thefluid flow is controlled throughout the gearbox. The present inventionuses a bypass block, described in further detail hereinbelow, to limitthe pressure within the pressurized gearbox during cold starts and otherconditions that may result in excess pressure. During a cold start, thatis when the lubrication fluid has not warmed and during which it is at amaximum viscosity, pressure can damage the gearbox do to the extremehigh pressure created as a result of attempting to flow a very viscousfluid through a lubrication pump and into the oil filter. The highpressure during cold start-up leads to reduce life for the lubricationpump, the oil filter, and/or the gearbox and can also lead to highercomponent design requirements due to the excess pressures encountered.

FIG. 1 shows an aircraft 100 in accordance with a preferred embodimentof the present application. In the exemplary embodiment, aircraft 100 isa helicopter having a fuselage 102 and a rotor system 104 carriedthereon. A plurality of rotor blades 106 is operably associated with arotor system 104 for creating flight. A tail boom 108 is depicted thatfurther includes tail rotor 110.

For example, FIG. 2 shows a partial cross-section perspective view ofaircraft 100 that includes additional detail of the present invention.Aircraft 100 further includes a main rotor mast 112, which is connectedto the main rotor gearbox (MRGB) 114. The MRGB 114 is connected to oneor more accessory gear boxes 116, one or more reduction gearboxes (RGB)216 a, 216 b, hydraulic pump(s) and generator(s). Each RGB 216 a, 216 bis connected to one or more engines 120 a, 120 b, which are within anengine compartment 118. A tail rotor drive shaft 122 transmitsmechanical rotation to the tail rotor gearbox 124, which is connectedvia tail rotor drive shaft 126 and intermediate gear box 128.

The drive system and subcomponents of aircraft 100 were developed toaddress the failures common to rotorcraft drive systems and is based ona completely new design and application of new technology to rotorcraftsafety. More particularly, the new rotorcraft drive system is focused inan unparalleled manner on safety and redundancy. The goal of safetydrove the design and development of the unique layout and configurationof the rotorcraft drive system described herein, which incorporatesunique features and system separation that protects primary aircraftsystems from the most common drive system failures. The drive system hasalso been designed to maximize the operational capability in the eventof an uncommon failure, such as a loss of lubrication.

The drive system and subcomponents of aircraft 100 overcome many drivesystem failures by including one or more of the following designfeatures: (1) minimize the number of single path drive systemcomponents; (2) provide maximum system separation and redundancy; (3)minimize maintenance requirements and maintenance related incidents; (4)minimize the potential of loss of lubrication events; and/or (5)maximize main rotor gearbox loss of lubrication capability. Therotorcraft drive system includes, e.g., dual engine reduction gearboxescompletely isolated from the remainder of drive system via freewheelingclutches in the main rotor gearbox, dual accessory gearboxes separatefrom the main rotor gearbox, and the distribution of the gearbox drivenaccessories among the separate systems, among other improvements.

High-speed gearing and the associated heat generation is always an areaof concern for gearbox survivability. The ability to continue torquetransmission, particularly in a loss of lubrication scenario, is ofgreat importance. For this reason, the drive system includes twoseparate RGB's, each one connected to a separate engine and independentfrom the MRGB. The reduction gearboxes are fully self-contained andseparate from each other, each reducing the engine output speed from ahigh speed at or near turbine engine speed of greater than 10,000 RPM toa speed substantially lower than the high speed, a low speed of lessthan about 6,000 RPM prior to transmitting torque to the MRGB. Each RGBhas its own self-contained lubrication system consisting of pump,filter, oil monitoring sensors, and a unique core in the aircraft coolerassembly. With this drive system arrangement high-speed gearing iscontained in separate gearboxes, as such, the survivability of the totaldrive system is greatly enhanced, particularly in the event ofhigh-speed gear failure or loss of lubricant in an individual RGB. Theuse of independent RGBs that connect to a single low speed overhungplanetary gear system in the MRGB reduces rotating part count and heatgeneration. With maintenance in mind, the drive system allows for ashort mast top case assembly that allows swapping of the top case andmast without removal of the main rotor gearbox from the aircraft. TheMRGB also includes a clutch for each of the reduction gearboxes thatallows each reduction gearbox to be separately and independentlydisconnected from the MRGB.

The drive system of aircraft 100 can also take advantage of a number ofadditional features that minimize the possibility of loss of lubricantand to maximize the operational time if a loss of lubricant event doesoccur. For example, the drive system can also include one or more of thefollowing: (1) the use of transfer tubes for cooler and filter mountingto eliminate the loss of lubricant in the event of loss of attachmentfastener torque; (2) using an oil cooler mounted directly to the MRGBeliminating external hoses; (3) the use of all oil filter bowls arescrew-on instead of held-on with small fasteners eliminating fastenerfailure issue from repeated removals; (4) the elimination of a highspeed planetary and the heat generation associated with it during a lossof lubrication event; (5) the use of gear tooth geometry specificallydesigned to minimize sliding reducing heat generation at the teeth andthe tendency to score during a loss of lubrication event; (6) the use ofcoarse pitch power gears with clearance or backlash allowing for theexpansion during high heat loss of lubrication events; (7) the use ofhigh hot hardness material utilized for primary torque carryingcomponents maximizing their continued operation in the event of a lossof lubrication event; (8) the use of ring gear and case joint design toefficiently transmit heat away from the planetary gears in the event ofa loss of lubrication event; and/or (9) the use of isotropic superfinished gear teeth resulting in a greatly improved surface finish andmaximizing the ability of these gears to operate in a reducedlubrication environment.

FIG. 3 shows an isometric view of a gearbox lubrication system 200 thatshows the position of the pressure relief bypass block 204 of thepresent invention. More particularly, the gearbox 202 includes thepressure relief bypass block 204 on the gearbox 202, in relation to anoil filter 206 and the oil cap 208.

FIG. 4 shows a contralateral isometric view of the gearbox lubricationsystem that shows the position of the pressure relief bypass block 204of the present invention. More particularly, the gearbox 202 includesthe bypass block 204 on the gearbox 202, in relation to an oil filter206.

FIG. 5 shows a cross-section view of the bypass block 204 of the presentinvention. The pressure relief bypass block 204 includes an inlet 210through which the lubrication fluid enters the pressure relief bypassblock 204. The inlet is in fluid communication with a pressure-reliefvalve 212, which opens to relieve excess fluid pressure in the pressurerelief bypass block 204 such as from the lubricant entering at a lowtemperature and high viscosity at bypass outlet 214. The pressure-reliefvalve 212 can be a mechanical pressure-relief valve, such as a pop-itvalve or equivalent, can be electronically or magnetically actuated. Thepressure-relief valve 212 is maintained open while pressure is at anypressure greater than the component is designed for. Whenpressure-relief valve 212 is bypassing, fluid entering the oil filter islimited to the set bypass pressure. This fluid is bypassed from 210,through 212, to exit through 214. When pressure drops, andpressure-relief valve 212 closes, fluid enters filter from 210 and exitslubricant exit 217.

FIG. 6A is a close-up, cross-sectional view of a pressurized filter 300that is lacking the bypass of the present invention and is connected togearbox 302. The gearbox 302 includes a high pressure lubricating fluid304 that enters the filter 300 at high pressure 306 and exits thefilter, also at high pressure 308.

FIG. 6B shows a close-up, cross-sectional view of a pressurized filter400 that includes a bypass block 410 of the present invention and isconnected to the unregulated pressurized gearbox 402. The bypass block410 is contained within a block, manifold, or housing that is separatefrom the gearbox housing or filter housing. The bypass block 410 can beprovided in the form of a kit that is used to retrofit, and fit with,existing filter and gearbox housing combinations. The bypass block,manifold, or housing kit can include, e.g., gasket(s) and longer screwsthat account for the added thickness of the bypass block, manifold, orhousing. The bypass block 410 may be added to previously designedpressure lubricated gearboxes or in a newly designed pressure lubricatedgearbox in which limiting the high pressure is beneficial. High pressurelubricant fluid 404 exits the unregulated pressurized gearbox 402 andenters the bypass block 410 at lubricant inlet 411, and the highpressure lubricating fluid is returned to the unregulated pressurizedgearbox 402 through the bypass valve 413 at high pressure at the bypassoutlet 406. As the pressure of the lubricating fluid drops, the bypassvalve 413 closes and the low pressure lubricating fluid 414 enters thepressurized filter 400 at the low-pressure outlet 412, and exits thepressurized oil filter 400 at the lubricant exit 416. Thus, after thepressure of the lubricating fluid drops in the unregulated pressurizedgearbox 402, it does so within the pressurized filter 400, and the lowpressure lubricating fluid 414 exits the filter 400 back into theunregulated pressurized gearbox through the lubricant exit 416.

It will be understood that particular embodiments described herein areshown by way of illustration and not as limitations of the invention.The principal features of this invention can be employed in variousembodiments without departing from the scope of the invention. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, numerous equivalents to the specificprocedures described herein. Such equivalents are considered to bewithin the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specificationare indicative of the level of skill of those skilled in the art towhich this invention pertains. All publications and patent applicationsare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.” Throughout this application, the term “about” is used toindicate that a value includes the inherent variation of error for thedevice, the method being employed to determine the value, or thevariation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps. In embodiments of any of the compositions andmethods provided herein, “comprising” may be replaced with “consistingessentially of” or “consisting of”. As used herein, the phrase“consisting essentially of” requires the specified integer(s) or stepsas well as those that do not materially affect the character or functionof the claimed invention. As used herein, the term “consisting” is usedto indicate the presence of the recited integer (e.g., a feature, anelement, a characteristic, a property, a method/process step or alimitation) or group of integers (e.g., feature(s), element(s),characteristic(s), propertie(s), method/process steps or limitation(s))only.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation,“about”, “substantial” or “substantially” refers to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skilled in the art recognizethe modified feature as still having the required characteristics andcapabilities of the unmodified feature. In general, but subject to thepreceding discussion, a numerical value herein that is modified by aword of approximation such as “about” may vary from the stated value byat least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

All of the devices and/or methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the devices and/or and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and/or methods and in the steps or in the sequence of stepsof the method described herein without departing from the concept,spirit and scope of the invention. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the disclosure. Accordingly, the protection soughtherein is as set forth in the claims below.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

What is claimed is:
 1. A method for reducing lubricant damage to anexisting combination of an unregulated pressurized gearbox and apressurized filter comprising: providing a bypass block comprising abypass valve, a lubricant inlet in fluid communication with the bypassvalve, a bypass outlet in fluid communication with the bypass valve, alow-pressure outlet in fluid communication with the bypass valve, and alubricant exit, wherein the bypass block is separate from a housing ofthe unregulated pressurized gearbox and is attached to the unregulatedpressurized gearbox and the pressurized filter such that the bypassvalve is upstream from the pressurized filter, the lubricant inlet is influid communication with the unregulated pressurized gearbox, the bypassoutlet is in fluid communication with the unregulated pressurizedgearbox, the low-pressure outlet is in fluid communication with thepressurized filter, and the lubricant exit is in fluid communicationwith the pressurized filter and the unregulated pressurized gearbox;diverting a lubricant at temperatures or pressures within predeterminedbypass valve ranges into the unregulated pressurized gearbox through thebypass outlet to reduce damage to the pressurized filter from highpressure; and allowing the lubricant at temperatures or pressuresoutside the predetermined bypass valve ranges into the pressurizedfilter through the low-pressure outlet.
 2. The method of claim 1,wherein the unregulated pressurized gearbox is an intermediate gearbox,a tail rotor gearbox, or a reduction gearbox.
 3. The method of claim 1,wherein the relief valve is at least one of: mechanical, electronic,magnetic, or spring-loaded.
 4. The method of claim 1, wherein the reliefvalve is a pressure or temperature activated valve.
 5. The method ofclaim 1, wherein the relief valve is a pressure relief valve.
 6. Themethod of claim 1, wherein the relief valve is a pressure relief valve,a pressure release valve, a pressure safety valve, a safety reliefvalve, a pilot-operated relief valve, a snap acting release valve, apop-it valve, or a modulating release valve.
 7. A method for reducinglubricant damage to an existing combination of an unregulatedpressurized gearbox and a pressurized filter comprising: providing abypass block comprising a bypass valve and a lubricant inlet in fluidcommunication with the bypass valve, wherein the bypass block isseparate from a housing of the unregulated pressurized gearbox andattached to the unregulated pressurized gearbox and the pressurizedfilter, and the bypass block is upstream from the pressurized filter;and diverting a lubricant into the unregulated pressurized gearbox orinto the pressurized filter, wherein the lubricant is returned to theunregulated pressurized gearbox when the lubricant is cold and pressureat the bypass valve is high to reduce damage to the unregulatedpressurized gearbox caused by high pressure during a cold start, andwhen the lubricant temperature increases and the pressure is reduced thevalve closes and the lubricant enters the pressurized filter.
 8. Themethod of claim 7, wherein the unregulated pressurized gearbox is anintermediate gearbox, a tail rotor gearbox, or a reduction gearbox. 9.The method of claim 7, wherein the relief valve is at least one of:mechanical, electronic, magnetic, or spring-loaded.
 10. The method ofclaim 7, wherein the relief valve is a pressure or temperature activatedvalve.
 11. The method of claim 7, wherein the relief valve is a pressurerelief valve.
 12. The method of claim 7, wherein the relief valve is apressure relief valve, a pressure release valve, a pressure safetyvalve, a safety relief valve, a pilot-operated relief valve, a snapacting release valve, a pop-it valve, or a modulating release valve.